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Rabbit killers

AT LEAST ten species of insect may be carrying the deadly rabbit calicivirus
around Australia, population biologist Brian Cooke told ANZAAS.

Cooke works in Canberra at the Division of Wildlife and Ecology, part of the
CSIRO, Australia’s national research agency. He says that the virus has recently
been found in five species of blowfly, a carrion fly, two kinds of mosquito and
the European rabbit flea.

How the virus has spread round Australia has been a mystery since it escaped
during trials on Wardang Island off South Australia in October 1995—though
the Australian bushfly was fingered as the guilty party at the time.

It now appears that the bushfly is just one of many possible insect vectors.
Cooke says that levels of virus in rabbit blood are high enough for it to be
transmitted by biting insects. Experiments are now under way to see if the virus
can be spread by infected flies defecating or vomiting on vegetation eaten by
rabbits.

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The main vector must be very common and fast moving. In arid and semiarid
areas of Australia, the virus is spreading at a rate of up to 100 kilometres a
week.

But why its spread is patchy in more humid areas remains a mystery. In some
wet areas, up to 80 per cent of rabbits are being killed, but just 50 kilometres
away few rabbits are dying. “We are not sure what is going on,” says Cooke.

Cooke also told ANZAAS that there is nothing to suggest the virus is
spreading to other mammals. “Foxes form antibodies to the virus because they get
such a massive dose when they eat diseased rabbits, but there is no evidence of
them expressing the virus itself,” he says.